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CHICAGO - Here's a health tip in a nutshell: Eating a handful of nuts a day for a year — along with a Mediterranean diet rich in fruit, vegetables and fish — may help undo a collection of risk factors for heart disease.

Spanish researchers found that adding nuts worked better than boosting the olive oil in a typical Mediterranean diet. Both regimens cut the heart risks known as metabolic syndrome in more people than a low-fat diet did.

"What's most surprising is they found substantial metabolic benefits in the absence of calorie reduction or weight loss," said Dr. JoAnn Manson, chief of preventive medicine at Harvard's Brigham and Women's Hospital.

In the study, the people who improved most were told to eat about three whole walnuts, seven or eight whole hazelnuts and seven or eight whole almonds. They didn't lose weight, on average, but more of them succeeded in reducing belly fat and improving their cholesterol and blood pressure.

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Manson, who wasn't involved in the study, cautioned that adding nuts to a Western diet — one packed with too many calories and junk food — could lead to weight gain and more health risks. "But using nuts to replace a snack of chips or crackers is a very favorable change to make in your diet," Manson said.

Nuts help people feel full while also increasing the body's ability to burn fat, said lead author Dr. Jordi Salas-Salvado of the University of Rovira i Virgili in Reus, Spain.

Nuts are rich in anti-inflammatory substances, such as fiber, and antioxidants, such as vitamin E. They are high in unsaturated fat, a healthier fat known to lower blood triglycerides and increase good cholesterol.